Studies in this laboratory are designed to elucidate the role of DNA repair processes in human diseases and in carcinogenesis and in normal and abnormal aging. Most studies have been conducted with cells from patients with xeroderma pigmentosum (XP) who have defective DNA repair plus multiple cutaneous malignancies, and premature aging of sun-exposed skin and of the nervous system. Cells from patients with ataxia telangiectasia and tuberous sclerosis, diseases with abnormal cell growth and differentiation, and from patients with primary neurological degenerations are also being studied. These studies are designed to elucidate the pathogenesis of these disorders as well as to develop presymptomatic diagnostic tests. We assess the biological effectiveness of DNA repair primarily by in vitro assays of cell survival after treatment of the cells with the DNA damaging agents.